a) Field of the Invention
The present invention relates to optical path converting optical elements, optical converters, as well as optical projectors and image display apparatuses using such optical elements.
b) Related Art
(First example)
A structure of an example of a liquid crystal projector 1 is shown in FIG. 1. This liquid crystal projector 1 employs an integrator lens 5 to provide a uniform luminance distribution. The principle of this luminance distribution adjustment is shown in FIGS. 2(a) to 2(c).
This liquid crystal projector 1 is constructed as follows. An integrator lens (lens array) 5, a field lens 6, and a condenser lens 7 are arranged ahead of a subsurface illuminator 4 that is constructed of a lamp 2 and a parabolic reflector 3. A liquid crystal display panel 8 is arranged ahead of the condenser lens 7, and a projector lens 10 is arranged ahead of the liquid crystal display panel 8.
Thus, in the liquid crystal projector 1 that is constructed as shown in FIG. 1, light rays r that have been injected rearward from the lamp 2 and reflected by the reflector 3 enter into the integrator lens 5 as substantially parallel rays. As shown in FIG. 2(b), a luminous intensity distribution in a direction (X-axis direction) perpendicular to the optical axis of the light rays r before entering into the integrator lens 5 becomes maximum on the optical axis and drastically reduces as the light rays deviates from the optical axis. That is, it is bright in the middle and dark in the periphery. The field lens 6 is arranged slightly ahead of the focal points of the respective lens element regions of the integrator lens 5, and the condenser lens 7 is arranged at the focal point of the field lens 6. As a result, the light rays r that have passed through the respective lens element regions of the integrator lens 5 are condensed by the respective lens element regions of the integrator lens 5, then enter into the field lens 6 as dispersed light rays, and are irradiated onto the entire part of the condenser lens 7 as shown in FIG. 2(a). Then, the light rays r that have been collimated by the condenser lens 7 pass through the liquid crystal display panel 8, and an image generated by the liquid crystal display panel 8 is projected onto a screen 11 via the projector lens 10.
Since the light rays r having different luminous intensities which have passed through the different lens element regions of the integrator lens 5 are synthesized by the condenser lens 7 this way, the light rays r having an ununiform luminous intensity distribution are converted into light rays having a uniform luminous intensity distribution by passing through the optical system including the integrator lens 5, the field lens 6, and the condenser lens 7 as shown in FIG. 2(c), and thereafter enter into the liquid crystal display panel 8. As a result, the luminance distribution of an image projected onto the screen 11 becomes also uniform.
(Second example)
FIG. 3 shows an example of an image display apparatus 16 which uses a microlens to improve luminance. As shown in FIG. 3, this image display apparatus 16 has a microlens array 17 arranged so as to confront the liquid crystal display panel 8. The liquid crystal display panel 8 is formed by sealing a liquid crystal material 23 between a glass substrate 21 and a glass substrate 22. The glass substrate 21 has a black matrix region 19 having wirings and the like for driving TFTs 18, transparent electrodes 20, and the like formed thereon. The glass substrate 22 has a total surface common electrode formed thereon. The transparent electrode (20) portions surrounded by the black matrix region 19 serves as pixel holes 24. Lenses 25 forming the microlens array 17 are arranged so as to confront the pixel holes 24, respectively.
Thus, if the microlens array 17 is not employed, part of light rays r that have entered into the liquid crystal display panel 8 are shielded by the black matrix region 19 as shown in FIG. 4. Therefore, light utilization efficiency is reduced, which in turn reduces the luminance of the image display apparatus 16. In contrast thereto, if the microlens array 17 is employed, light rays r that have entered into the respective lenses 25 of the microlens array 17 are condensed onto the respective pixel holes 24 of the liquid crystal display panel 8 as shown in FIG. 5. That is, all the light rays having entered into the liquid crystal display panel 8 can be transmitted through the pixel holes 24. As a result, light utilization efficiency can be improved by utilizing the microlens array 17, and the luminance of the image display apparatus 16 can be improved.
In view of the aforementioned examples, it is conceivable to manufacture an image display apparatus 16 having a high luminance distribution as well as a uniform luminance distribution if the microlens array 17 is interposed between the optical system and the liquid crystal display panel 8 such as shown in FIG. 2(a).
However, when the optical system constructed of the integrator lens 5, the field lens 6, and the condenser lens 7 is used, the diffusing angle .theta. of the light that has passed through the condenser lens 7 becomes wide (see FIG. 2(a)). Therefore, light rays r such as indicated by broken lines in FIG. 5 are shielded by the black matrix region 19, so that the light rays cannot be condensed onto the pixel holes 24 by the microlens array 17 effectively.
Moreover, if the optical system such as shown in FIG. 2(a) is employed, the optical system becomes complicated. Since the field lens 6 must be arranged, the image display apparatus 16 becomes expensive.